The goals of this project are to develop measures for studying speech perception impairments in healthy younger adults with normal hearing and without developmental disorders and to obtain a database of individual differences measures to analyze in relationship to experimental measures. Healthy adults with speech perception impairments may present at an audiology clinic complaining of difficulty perceiving speech under degraded listening conditions, yet upon examination they are found to be audiologically normal. But speech-in- noise testing confirms their complaint. They may then be considered for a clinical diagnosis of central auditory processing disorder (CAPD), but there is not agreement as to how to diagnosis CAPD; there are no standard tests of CAPD; and unknown even is whether its cause is a disorder of auditory processing. No neural bases have been confirmed. Cognitive neuroscience offers a framework for investigating the neural bases for speech perception impairment (SPI) in otherwise healthy young adults. We hypothesize those individuals who complain of speech perception difficulties exist on a continuum of individual differences. We hypothesize that the neural mechanisms responsible for the SPI could arise singly or in interaction at the levels of stimulus representation, attention, and working memory. A delayed recognition memory paradigm will be developed to investigate these mechanisms. The paradigm is designed to obtain behavioral and electrophysiological (EEG) measures in response to speech. Healthy adults with normal hearing and with SPI will be recruited for study and compared to similar age normal adults without speech perception impairments. All participants will undergo a battery of audiological tests and other screening, including tests for verbal intelligence, mental status, and phonological working memory. Then they will be tested in the proposed delayed recognition memory paradigm to gain behavioral and EEG results related to working memory, attention, and speech stimulus encoding. Stimuli will be nonsense syllables or real words that are either natural recordings or vocoded. Extensive individual differences and group statistical analyses will be carried out using the EEG, behavioral, and clinical measures. Individual differences scores will be sought across normal and SPI groups and as reliable predictors of group membership. With better understanding of neural mechanisms responsible for differences in speech perception across groups and individuals, clinical evaluations can become more accurate and treatments can be developed. We envision carrying this project forward to develop clinical tests for adults and also children.